Safety and efficacy of DB-1303 in patients with advanced/metastatic solid tumors: A multicenter, open-label, first-in-human, phase 1/2a study.
Authors: Kathleen N. Moore, Dhanusha Sabanathan, Yiqun Du, Huaxin Duan, Xiumin Li, Feng Wang, Omkar Marathe, Hua Yang, Vicky Makker, Whitfield Growdon, Jim Coward, Peng Zhao, Liming Liu, Rong Shi, Shengxue Liu, Wei Gu, Yang Qiu, Zhongyuan Zhu, Jian Zhang, Erika P. Hamilton
Journal: Journal of Clinical Oncology (2023)

3023 Background: DB-1303 is an antibody-drug conjugate (ADC) consisting of a humanized anti-HER2 IgG1 monoclonal antibody, covalently linked to proprietary DNA topoisomerase I inhibitor (P1003) via a maleimide tetrapeptide-based cleavable linker, with a high drug-to-antibody ratio (~8). Methods: This is a global first-in-human, dose-escalation and -expansion study in patients (pts) with advanced/metastatic solid tumors. Pts (ECOG 0-1) with HER2 – (high or low) expressing or mutant cancers who failed previously systemic therapies were recruited and received DB-1303 intravenously Q3W as monotherapy. The objectives were safety, tolerability, maximum tolerated dose (MTD) or recommended phase 2 dose (PR2D), pharmacokinetics (PK), and preliminary antitumor activity. Here we report the results from dose-escalation. Results: As of Jan 13, 2023, 85 pts received DB-1303 at 6 dose levels (2.2, 4.4, 6.0, 7.0, 8.0, and 10.0 mg/kg) and received a median of 7 (range, 1-27) prior lines of therapy, including previous anti-HER2 ADC therapy in 32.9% of pts. The median duration of treatment was 63.0 (range, 21-211) days, and 68 pts (80.0%) remained on treatment. Treatment-emergent adverse events (TEAEs) and ≥ grade (G) 3 TEAEs occurred in 74 pts (87.1%) and 18 pts (21.2%), respectively; the most common TEAEs were nausea (51.8%, 3.5% ≥ G3), vomiting (43.5%, 1.2% ≥ G3), platelet count decreased (35.3%, 3.5% ≥ G3), and anemia (29.4%, 5.9% ≥ G3). Few pts experienced neutropenia (10 [11.8%]) and alopecia (3 [3.5%]). There was no DLT or TEAEs leading to death. Interstitial lung disease occurred in 2 pts (2.4%, G1), without any ≥ G2. The exposure parameters (C max and AUC) of DB-1303 ADC increased with ascending doses from 2.2 to 10.0 mg/kg. The half-life of DB-1303 ADC is approximately 6-7 days for 6.0-8.0 mg/kg dose cohorts. The exposure of serum release payload was magnitudes lower than that of DB-1303 ADC, demonstrating stability of the ADC in systemic circulation. A total of 52 pts had undergone at least one post-baseline tumor scan. Twenty-three pts (44.2%, 23/52) had objective partial tumor response per RECIST 1.1: Thirteen HER2+ breast cancer (BC) (50.0%, 13/26, including 5 pts with brain metastases [55.6%, 5/9]), 5 HER2 low BC (38.5%, 5/13), 2 colorectal cancer (66.7%, 2/3), 1 endometrial carcinoma (33.3%, 1/3), 1 esophageal cancer (50.0%, 1/2), and 1 ovarian cancer (50.0%, 1/2). Among all the pts, the DCR was 88.5% (46/52); for pts with HER2+ BC and HER2-low BC, the DCRs were 96.2% (25/26) and 84.6% (11/13), respectively. Conclusions: DB-1303 was well tolerated with encouraging preliminary antitumor activity in heavily pretreated pts with advanced/metastatic solid tumors, especially in pts with HER2+ BC and brain metastasis as well as in HER2-low BC. Expansion is ongoing in selected tumor pts treated at the RP2D. Clinical trial information: NCT05150691 .